Detect SquashFS errors and alert the user about them

Just a Daemon that detects SQUASHFS errors from journalctl.

To trigger the squashfs error handling you can use a early_patch hook with:

#!/bin/sh
# Make sure that there are SQUASHFS errors "to detect"
touch $root/var/lib/live/tails.squashfs_failed

# disable service, as the service would delete the magic file if now errors are found.
rm $root/etc/systemd/system/multi-user.target.wants/tails-detect-squashfs-errors.service

failure detected before gdm is started:

refs #5856 (closed) refs #16030 (closed)